This invention relates to a propeller shaft having male and female shafts, each having at one end a yoke and at the other end a spline sliding portion to be fitted with each other and a method for producing such a propeller shaft. More particularly, the invention relates to a method for forming a phase indexing reference of spline shafts including steps of forming an irregular portion on part of spline teeth of a regular female spline tooth pattern of a female shaft, and forming an irregular portion on part of spline teeth of a regular male spline tooth pattern of a male shaft, these irregular portions being able to be fitted with each other when the male and female shafts coincide in phase of spline teeth with each other.
In producing such a propeller shaft in the past, a hollow tube has been generally cut into a required length for the shaft as shown in FIG. 1a, and a spline toothed member 2 and a yoke 3 have been brought into engagement with respective associated ends of the cut hollow shaft 1 and connected thereto as by welding as shown in FIG. 1b. A solid bar member has been generally worked by rolling or tooth cutting or hobbing to form a spline toothed member 2 for a male shaft, or by broaching to form a spline toothed member 2 for a female shaft.
In such a hitherto used producing method, it was needed to press-fit the spline toothed member 2 and the yoke 3 into the respective ends of the length adjusting hollow tube 1 and then to join them at joint positions 4 by electric welding or friction welding. Therefore it took much time for producing the propeller shaft, and after thus joined, the accuracy of the shaft as a whole often became insufficient, even with each high individual accuracy of the respective element members 1, 2 and 3.
In more detail, these element members 1, 2 and 3 are not machined by the same apparatus, but are produced in exclusive apparatuses or areas, respectively, causing much economical losses.
Moreover, as the produced propeller shaft is a combined body made of the separate members 1, 2 and 3, there is a tendency for the propeller shaft to be joined in an incorrect condition, with angular displacement in phase, eccentricity, bend or curve, and the like, with the result that uneven rotation and unbalance may be caused to reduce the durability of the propeller shaft and generate strange sound and vibration in operation. As a result, an amending operation for the produced propeller shaft is needed in order to improve its accuracy to a required level.
Furthermore, the male shaft is worked to form its spline by rolling, tooth cutting, or broaching so that chips are produced to cause losses of material, reduction in strength and environmental pollution. Moreover, these working operations may in general obstruct the production of a light-weight propeller shaft, and the solid male shaft of a propeller shaft increases its weight.
In assembling spline shafts, in general, after yokes of male and female shafts are brought into angular coincidence with each other, the spline toothed portions of the male and female shafts are slidably connected to each other. Due to the multiplicity of the spline teeth, however, there is a risk of spline shafts being assembled with displaced angular phase without careful operation for bringing the male and female shaft in angular coincidence in angular phase with each other. If there is such a displacement in phase, the difference in phase between input and output sides causes changes in rotation and torque and hence causes noise and vibration, resulting into reduction of service life.
There have been various methods for forming phase indexing references for spline shafts in order to facilitate the assembling of them as shown in FIGS. 2a, 2b, 3a, 3b, 4a and 4b.
In FIGS. 2a and 2b, spline teeth of a female shaft 11 are formed to have an irregular portion 12 at one bottom between adjacent two spline teeth of a regular pattern of the female shaft 11. The irregular portion 12 is a shallower bottom than the other bottoms 13 between the other spline teeth. On the other hand, spline teeth of a male shaft 14 are formed to have an irregular portion 15 at one of spline teeth of a regular pattern of the male shaft 14. The irregular portion 15 is a lower tooth adapted to be fitted in the irregular portion 12 of the female shaft 11 when the male and female shafts coincide in phase with each other. The irregular portion 15 of the male shaft 14 corresponds to the "phase indexing reference". In this case, the spline of the female shaft is finished by broaching, while the spline of the male shaft is finished by milling.
In FIGS. 3a and 3b, spline teeth of a female shaft 11 are formed to have an irregular portion 16 at one tooth of a regular pattern of a female shaft 11. The irregular portion 16 has a form in which one tooth is removed to connect or merge two bottoms on both sides of the removed tooth into a widened bottom as an irregular portion 16. Two diametrically opposed irregular portions 16 may be provided as in another example shown in FIG. 4a and 4b. These spline teeth of particular patterns are finished by broaching. As shown in FIGS. 3b and 4b, a filling 17 as an irregular portion is provided in the bottom between two spline teeth of an irregular pattern of a male shaft 14 corresponding to the irregular portion 16 of the female shaft 11. The filling 17 is formed by spot welding so as to have a height not higher than that of the other spline teeth of the male shaft 14.
With the method shown in FIGS. 2a and 2b, it is difficult to work only one spline tooth of the male shaft 14 by tooth cutting to form the irregular portion. Moreover, with the method shown in FIGS. 3b and 4b, the filling 17 tends to fall off in use.